1. Field of the Invention
This invention relates to water-based adhesives, coatings and primers. Specifically, it relates to water-based polyurethane compositions having improved characteristics such as adhesion, peel strength and heat resistance. More specifically, it relates to one-component water-based sulfonated polyurethane compositions useful as adhesives, coatings and primers in the manufacture of footwear and to footwear and a method of preparing footwear using such compositions.
2. Description of the Prior Art
It is generally known that water-based sulfonated polyurethanes are useful in the manufacture of footwear. References describing such include the following:
U.S. Pat. No. 5,334,690 (Hoechst Aktiengesellschaft, Fed.) discloses water-based sulfonated polyurethanes which are obtained by reacting ionic polyester polyols, polycarbonate polyols and polyether polyols or mixtures thereof with a polyisocyanate or mixtures of polyisocyanates. The water-based sulfonated polyurethane special feature are the ionic groups present in the polyol segment. These polymers are described as being especially useful in the production of adhesive bonds for the shoe industry.
German Pat. No. DE 3930352 (REIA GMBH) discloses a process for bonding parts of shoes by applying water-based sulfonated polyurethane adhesives and drying with a microwave heater before bringing the parts together. The water-based sulfonated polyurethane Dispercoll U KA-8464 from Bayer Corporation is referenced.
"Waterbased high performance adhesive materials", Warrach., Presented at Proceedings of the ASC Division of Polymeric Materials Conference, Miami Beach, Fla., Sep. 11-18, 1989. The article describes water-based sulfonated polyurethane polymers, and their formulations, yielding good adhesion to substrates often used in the manufacture of footwear like PVC, ABS, polyurethanes, nylon, leather and fabrics.
A draw back for these prior art compositions is their failure to pass minimum adhesion standards in footwear applications, set by the Association of European Adhesive Manufacturers (FEICA), as one-component formulations. To pass minimum adhesion standards, two-component adhesive formulations are required. For example, bond strengths when subjected to thermal and mechanical stresses can be improved by the addition of water dispersible polyfunctional crosslinking agents selected from a group consisting of isocyanates, aziridines, melamine resins, epoxies, oxazolines and carbodiimides. However, a disadvantage associated with two component formulations is their limited pot life due to coagulation, gelling and viscosity increase. Furthermore, two-component adhesives have to be mixed from separate components directly before use. This can give rise to unsatisfactory adhesive bonds or a shortened pot life through inexact metering of the components making the system less user friendly. Also, exposure to latent crosslinking agents can pose a health risk through skin contact or inhalation.
There remains a need for improved one-component water-based adhesives, coatings and primers. One-component water-based compositions are easier to handle, safer and generally cost less. The present inventors have now discovered new one-component water-based sulfonated polyurethane adhesives compositions which pass FEICA minimum specifications for sole bonding. The present inventors have also discovered two-component water-based sulfonated polyurethane compositions having improved performance over previously known two-component systems.